But 15-year-old Alaa Yasser was not among them. Instead, he was working at a nearby car shop to support his family.

"I had to stop going to school to work with my father to help him earn a living," said Yasser, whose family fled the southwestern city of Taez.

Two million children across the country have no access to education, according to the UN children's agency UNICEF, three years into a war that has pushed Yemen to the brink of famine and shows no sign of waning.

Millions of children across the world miss out on school as a result of humanitarian emergencies including conflicts, natural disasters and health crises. Education can be lifesaving - not being in school in emergencies can leave children at risk of child labour, early marriage, exploitation and recruitment into child labour.